Hot vs. cold water steeping of different teas: Do they affect antioxidant activity?

摘要

A new popular way of making tea, especially in Taiwan, is to steep leaves in cold water. Here we investigate whether antioxidant activity of teas may be affected by hot or cold water steeping and if this correlates with their polyphenol content and metal-chelating activity. A set of five loose tea samples, consisting of unblended and blended teas, was analysed following their infusion in either hot water (90 ℃, 7 min) or cold water (room temperature, 2 h). Antioxidant activity, measured as hydrogen-donating ability, using the ABTS and DMPD assays, showed no significant differences among hot or cold teas, except in the case of white tea, where significantly higher values were obtained after cold water steeping, a recurrent finding in this study. The antioxidant activity of the teas correlates well with their total phenolic content and metal-chelating activity. Cold teas were, however, generally better inhibitors of in vitro LDL conjugated diene formation and of loss in tryptophan fluorescence. The results of this study contribute to gaining further knowledge on how the potential health benefits of this popular beverage may be maximised by the different methods of preparation.